In hydraulic drives which serve to operate a technical process, the hydraulic drive may have have a specific velocity profile. The hydraulic drive acts on the technical process in a stipulated desired drive speed.
On the one hand, it is possible, in particular, to control the hydraulic drive with reference to its operating speed by means of a closed-loop control circuit. The disadvantage of such closed-loop control circuits consists in that the control requires a precise, quick and therefore technically complicated sensor technology and control engineering. The sensor technology serves to detect specific measured values, required as input variables of the closed-loop control circuit, of the hydraulic drive, such as, for example, specific pressures, valve strokes and drive speeds.
Three different closed-loop concepts, specifically state control, adaptive control and structurally variable model follower control are described in Kxc3x6ckemann, A, Konertz, J, Lausch, H. xe2x80x9cRegelung elektrohydraulischer Antriebe unter Berxc3xccksichtigung industrieller Rand-bedingungenxe2x80x9d xe2x80x9cClosed-loop control of electrohydraulic drives taking account of industrial boundary conditionsxe2x80x9d; at xe2x80x94Automatisierungstechnik, 1991, No. 6, pages 187 to 196. Furthermore, a digital closed-loop control of plastics injection molding machines is described in Pritschow, G Dalacker, M, Treffler, V.: xe2x80x9cHochdynamische digitale Regelung von Kunststoffspritzgiexcex2maschinenxe2x80x9d, xe2x80x9cHighly dynamic digital closed-loop control of plastics injection molding machinesxe2x80x9d; O+P xe2x80x9cxc3x96lhydraulik und Pneumatikxe2x80x9d, 1993, No. 6, pages 528 to 531 . In these closed-loop control circuits, the closed-loop control likewise requires a corresponding sensor technology and control engineering.
German Patent No. DE 43 15 626 describes an open-loop control for a hydraulic drive, in which a desired value for moving the drive is calculated from a prescribed desired value. In this case, the calculation is based in each case at least on a measured state variable of the drive at the instant of the calculation.
It is an object of the present invention to provide a control method for a hydraulic drive which permits nonlinearities to be taken into account.
The object is achieved with the aid of the control method according to the present invention, and with the aid of the plastics injection molding machine according to the present invention, having an open-loop control circuit for carrying out the control method, and with the aid of the use of the control method for controlling a plastics injection molding machine.
The control method according to the present invention has the advantage that it is possible to take account of nonlinear dependencies of the hydraulic drive acting on the technical process in order to generate the manipulated variable driving the hydraulic drive. In this case, it is advantageously possible to dispense with a technically complicated sensor technology for measured-value acquisition.
It is particularly advantageous that in the control method according to the present invention account is taken both of properties of the hydraulic drive and of properties of the technical process, particularly internal resistance for which the technical process opposes to the hydraulic drive.
In an advantageous embodiment of the control method according to the present invention, the parameter simulating the internal resistance is cyclically updated. It is thereby advantageously possible for the control method to be switched over adaptively, in particular automatically, to changing, technical processes which are operated by the hydraulic drive.
It is therefore advantageously possible by using the control method according to the present invention in plastics injection molding machines, for example, to eliminate a troublesome heating and cooling phase before using a new plastics injection molding machine, since the cyclically performed updating can automatically take account of the changes in the technical process.
A further advantage is that the control method according to the present invention can be carried out by using a precontrol circuit in a closed-loop control circuit. An appropriate precontrol circuit can be used, for example, as support for a closed-loop control circuit. Whereas the control method according to the present invention takes over the coarse presetting of the hydraulic drive, the closed-loop control circuit serves the purpose of further, additional fine tuning. It is thereby possible for the accuracy and speed of the hydraulic drive to be improved.